Question

I receive PatternSyntaxException when try to compile the following regex:

"bd".matches("(a)?b(?(1)c|d)")

this regex matches bd and abc. It does not match bc.

any ideas? thanks.

ok i need to write regex to match next 4 strings:

*date date* date date1*date2

should not match:

*date* date1*date2* *date1*date2 date** ...

but this should be done with single matching, not several.

please do not post answer like:

(date*date)|(*date)|(date*)|(date)

Answer 1

Adding a new answer based on the OP’s edit and samples:

ok i need to write regex to match next 4 strings:
*date date* date date1*date2
should not match:
*date* date1*date2* *date1*date2 date** ...

If I think I understand you, you could use a regex based on Alan Moore pseudo conditional trick.

Something like this ^(?:[*]())?date(?:(?!\1)[*](?:date)?|)$ might work.
I am asuming ‘date’ is the only text in the samples, and each group of non-space characters in the samples are distinct lines of text.

In your text that passes, there is only one form that requires a pseudo conditional. That is ‘date*date’. So, I’ve included a Perl sample below (since I don’t have a Java compiler) that expands the regex for clarity.

use strict;
use warnings;

my @samps = qw(

*date
 date*
 date
 date*date
*date*
 date*date*
*date*date
 date**
);

for my $str (@samps)
{
   print "\n'$str'\n";

   if ($str =~
       /
        ^          # Begin of string
        (?:             # Expr grouping
            [*]()          # Asterisk found then DEFINE capture group 1 as empty string
        )?              # End expr group, optional, if asterisk NOT found, capture group 1 stays UNDEFined
        date   #  'data'
        (?:             # Expr grouping
            (?!\1)           # Pseudo conditional: If no asterisk (group 1 is UNDEF), then
            [*](?:date)?     # look for '*' folowed by optional 'data'
          |               # OR,
        )                    # Asterisk or not, should be nothing here
        $          # End of string
      /x)

     {
         print "matched: '$str'\n";
     }
}

Output:

'*date'
matched: '*date'

'date*'
matched: 'date*'

'date'
matched: 'date'

'date*date'
matched: 'date*date'

'*date*'

'date*date*'

'*date*date'

'date**'